1. Technical Field
The present invention relates to a method for manufacturing an actuator device and a liquid ejecting head. More specifically, the invention relates to a method of manufacturing an actuator device including a substrate, vibration plate, lower electrode and a piezoelectric element.
2. Related Art
Generally, actuator devices include a piezoelectric element that reacts when a voltage is applied, and can be used in a liquid ejecting head for ejecting liquid droplets. One example of a liquid ejecting head is an ink jet recording head. Typically, the ink jet recording head includes pressure generating chambers communicating with nozzle apertures, wherein part of the pressure generating chambers are made from a vibration plate. The vibration plate is moved by piezoelectric elements such that the ink in the pressure generating chambers is pressurized and discharged through the nozzle apertures. Currently, two types of ink jet recording heads generally used: one includes a longitudinal vibration mode piezoelectric actuator that expands and contracts in the axial direction of the piezoelectric element; the other includes a flexural vibration mode piezoelectric actuator.
In the former type, the volume of the pressure generating chamber can be changed by allowing the end of the piezoelectric element to knock against the vibration plate. Accordingly, this type is well-suited for high-density printing, but requires the additional steps of cutting the piezoelectric element into a comb teeth shape corresponding to the pitch of the nozzle apertures, and positioning the teeth so as to align with the respective pressure generating chambers. Unfortunately, this results in a complicated and expensive manufacturing process.
As for the latter type, piezoelectric elements can connect to the vibration plate by a relatively simple process in which a piezoelectric green sheet is put on the pressure generating chambers corresponding to the shape of the chambers and then fired. This type, however, requires a certain degree of area because the system requires the use of flexural vibration, making high-density configurations difficult to achieve.
In order to overcome the disadvantage of the latter type, another design has been proposed in which piezoelectric elements are independently associated with the respective pressure-generating chambers by forming a uniform piezoelectric material layer over the entire surface of the vibration plate using a film-forming technique. Next, the piezoelectric material layer is cut into a pattern corresponding to the shape of the pressure-generating chambers using lithography.
The piezoelectric material layer for the piezoelectric elements can be formed from lead titanate zirconate (PZT), for example. In this instance, when the piezoelectric material layer is fired, lead from the piezoelectric material layer is diffused into the silicon oxide (SiO2) film. This process forms a vibration plate on the surface of the flow channel silicon (Si) substrate. Unfortunately, however, the diffusion of lead lowers the melting point of the silicon oxide, and the silicon oxide may be undesirably melted by the heat used to form the piezoelectric material layer.
In order to solve this problem, the diffusion of lead from the piezoelectric material layer into the silicon oxide film can be prevented by forming an vibration plate comprised of zirconium oxide layer between the silicon oxide film and the piezoelectric material layer (for example, JP-A-11-204849). Unfortunately, the zirconium oxide film has low adhesion to the silicon oxide film, and the vibration plate is likely to separate.
More specifically, the zirconium oxide film is generally formed by depositing a zirconium film using a sputtering method and then thermally oxidizing the zirconium film. The resulting zirconium oxide film has a polycrystalline structure, and its crystals often bunch up together. Further, even if the zirconium oxide film contains columnar crystals, their proportion is low, meaning that the adhesion of the zirconium oxide film to the silicon oxide film is reduced, and the zirconium oxide film is prone to separate.
Accordingly, have been several methods proposed solving this problem. One includes a method for manufacturing an actuator in which the zirconium layer is preferentially oriented under specific conditions before thermal oxidation, and another discloses an actuator device having zirconium oxide preferentially oriented under specific conditions (for example, JP-A-2005-166719 and JP-A-2005-176433).
In practice, however, the adhesion varies even if the orientation is controlled, and satisfying actuator devices are not always achieved. This problem exists not only in the manufacturing process of actuator devices used in liquid ejecting heads, like ink jet recording heads, but also in the manufacturing process of actuator devices used in other apparatuses.